Structure solution of incommensurately modulated La6MnSb15

Abstract

Abstract La6MnSb15 is synthesized from the constituent elements in quartz ampoules at 973 K. Crucial for the quality of the obtained single-crystals was a slow cooling rate of 2 K h−1. The crystal structure of La6MnSb15 was investigated via single-crystal X-ray diffraction experiments, leading to the observation of superstructure reflections as described in the literature. Two crystals, with refined compositions of La6MnSb15 (1) and La6MnSb14.66(1) (2) were obtained from different batches, yet both showed an orthorhombic body centered unit cell as well as additional reflections at q 1 = (0,0,0.258(1)) for crystal (1) and q 1 = (0,0,0.244(1)) for crystal (2). The structure could be solved and refined in superspace group Immm(00γ)000 (71.1.12.1), leading to a concise structural model. Due to γ not being exactly 1/4, an incommensurate modulation is present in the presented compounds. In order to describe the structural influence of the modulation in 3D, different approximants were chosen and the differences compared. Additionally, the temperature dependence of the electrical resistivity was investigated, indicating a metallic behavior of the title compound. This result is in line with the retro-theoretical investigation in the literature that counts excess electrons when using the Zintl–Klemm–Busmann concept. 121Sb Mößbauer-spectroscopic investigations at 78 K show a broad signal with an average isomeric shift of δ ∼ −10 mm s−1, in line with a negatively charged Sb species. The massive line broadening can be explained by the large number of crystallographic antimony sites in the basic structure and the approximant.